1. Field of the Invention
The present invention relates to an optical information processing method and apparatus in which a light beam emitted from a light source is converged and irradiated onto an optical recording medium, thereby executing at least one of recording, reproducing, and erasing operations of information.
2. Related Background Art
Hitherto, as large capacity memories which are used in computers or the like, an optical card apparatus which can record and reproduce information, an optical disk apparatus, a magneto optical disk apparatus which can record, reproduce, and erase information, and the like have been known. In the above apparatuses, recording and the like are also executed by irradiating the light beam emitted from the light source onto an optical recording medium. At this time, an output power of a semiconductor laser or the like which is used as a light source fluctuates in association with environmental changes in temperature and the like even when a predetermined current is input. Therefore, in an apparatus disclosed in, for instance, U.S. Pat. No. 4,509,156, what is called an automatic power control (APC) in which an output power of a light source is detected upon reproduction and the result of the detection is fed back to the light source to thereby keep the output power constant is executed. On the other hand, in such an apparatus, upon recording, an input current value by the APC in the reproducing mode is held, the current of an amount corresponding to an increase in power which is necessary to record is added to the current held, and the resultant added current is supplied to the light source.
However, in the above APC, a certain extent of time period is necessary until the output power of the light source becomes stable. Therefore, in a case when the output power of the light source must be switched at a high speed, for instance, the powers of the light beam which are necessary to record or the like on an inner track portion and an outer track portion of, for instance, an optical disk differ and, further, in a case when random access of the light beam is executed in the region between those portions, the APC cannot sufficiently cope with such a case.
On the other hand, to solve the above inconvenience of the APC, there has been proposed an apparatus in U.S. Pat. No. 4,747,091 in which a light source is experimentally driven to emit the light prior to executing the recording operation or the like, the relation between a driving current of the light source and an output power is previously measured, and the result of the measurement is stored. According to such an apparatus, upon operation, the APC is not initially executed but a current of the stored value is supplied to the light source, thereby realizing a prompt switching of the light power.
However, in the measurement by the apparatus disclosed in U.S. Pat. No. 4,747,091, an accurate result is not always obtained. This is because different from the measuring mode, in the recording operation or the like, the light beam has been converged onto a medium and its reflected light is returned to the light source and an output of the light source is changed by the returned reflected light. That is, in the apparatus of U.S. Pat. No. 4,747,091, there is a concern of on occurrence of a difference of the relations between the driving current and the light power upon measurement before the operation and upon actual measurement.